Sealing rings used to confine fluids in gas turbine engines generally are required to repeatedly accommodate large variations in axial length due to the thermal expansions and contractions of the assemblies of which thy are a part. Also, they must not lose their resilience due to relaxation and they must avoid rupture due to metal fatigue. Sealing rings should also be pre-compressed to compensate for variations in the distance between the facing surfaces being sealed. These variations result from the accumulation of manufacturing tolerances, for example.
In the turbine nozzle section of an aircraft gas turbine engine, sealing rings must retain their resilience at temperatures at which the stress-relaxation characteristics of available deformable materials necessitate very low stress levels to resist metal fatigue. Thus, sealing rings that absorb the strain energy of deflection in bending may not be suitable in some high temperature applications. Halling U.S. Pat. No. 4,121,843 and Halling et al U.S. Pat. Nos. 4,457,523, 4,813,692 and 4,854,600 describe seals in which axial or radial displacements are converted to rotation of the seal cross-section to thereby reduce or eliminate bending stresses. These seals generally perform well but have practical disadvantages. For example, the seals in U.S. Pat. Nos. 4,813,692 and 4,854,600 require tooling and fixturing and/or tight tolerancing of mating parts to ensure engagement between a specified point on the seal section and the sealing cavity wall. Moreover, the seal described in U.S. Pat. No. 4,457,523 is not pressure-energized and thus may lose sealing capabilities when the pressure-differential is sufficiently high.
Pask et al U.S. Pat. No. 4,438,939 describes an annular seal in which belville washers are placed in opposing-hand pairs, with abutting peripheries joined by a U-section ring. This design is intended to allow the individual washers to vary their angular disposition with respect to each other to accommodate relatively large axial motion between two members being sealed. This is accomplished without creating bending stresses. A drawback, however, is that the sealing ring assembly is difficult to use in the confined space of an annular chamber. Also, the two washers have no interconnection to each other, but are instead joined by a separate ring. At higher pressure differentials, where a gap is created by lift-off of the sealing washer elements at their interface, limited leakage will occur through two parallel paths at the U-ring/conical washer interfaces. Moreover, the U-ring is necessarily of very small cross-section and is thus very flimsy in large diameters. This creates a danger of "spontaneous disassembly of the components during installation of the ring, where it sometimes may not be possible to see what has occurred due to deep insertion of mating components.